King led Latham in a two-way and multi-candidate GOP primary matchup, one that has the potential to become ideologically driven. However, Latham was the only Republican who led Democratic Rep. Bruce Braley in a hypothetical general election matchup to replace retiring Democratic Sen. Tom Harkin. Latham led Braley by 3 points, while King trailed him by 5 points.

None of these members of Congress have said whether they will seek the open Senate seat, but all three are believed to be interested in what could be among the most competitive races in 2014. CQ Roll Call currently rates the race as Leans Democratic.

In a two-way GOP primary, King led Latham 46 percent to 29 percent. In a race with Latham, conservative activist Bob Vander Plaats and two others, King’s edge shrinks significantly. In that scenario, King led with 31 percent, followed by Latham with 26 percent and Vander Plaats with 16 percent.

In the Democratic primary, Braley appears to be the only candidate with any significant level of name identification. He led with 50 percent, followed by two others with less than 4 percent support and about 43 percent of those polled not sure.

The autodial poll of 523 likely voters was conducted on Jan. 29 with a 4.3-point margin of error.